To use it, go into the early creature creator via the Create menu. (It doesn't replace the in-game one.)
The huts for use in the hut editor are parentless, like building parts.
The building editor part manipulators can be used in the hut editor. (Hold shift to freely move any part on the X and Z axes, hold ctrl to freely move any part on the Y axis)
Warning: Textures don't function outside of the editor if highrestexturelevel is enabled. Once enabled, there's no way to fix it other than restarting Spore.
Download: Outdated versions, for archival purposes: